290 Scientific Proceedings, Royal Dublin Society. 
It may here be remarked that during the time these observa- 
tions were being taken, on the 3rd and 4th October, there was no 
wind. 
In attributing, as I did, these changes of level to seismal 
influences, it would appear that the same impression was also first 
entertained by previous observers; the theories now held in con- 
nection with them are briefly as follows :— 
I. That they are caused by downward rushes of wind on the 
surface of the lake, accompanied by changes of barometric pres- 
sure. 
II. Dr. Forel attributes seiches to local variations of atmo- 
spherie pressure giving impulse, the effect of which would be 
apparent for a long time as a series of oscillations. He adds, how- 
ever, that he attributes seiches having a greater amplitude than 
1:5 metres to earthquake shocks. * 
III. In 1881, Mr. Plantamour, an authority on this subject of 
seiches, assured the writer of the article in “Encyclopedia Britan- 
nica” that he was utterly at a loss for a satisfactory explanation 
of their causes. 
IV. From the observations of Jallabert, Bertrand, Saussure, 
and Vaucher the following law, connecting seiches with movements 
of the barometer, has been deduced. ‘The amplitude of seiches is 
small when the atmosphere is at rest; the seiches are greater the 
more variable is the atmospheric pressure; they are the greatest 
when the barometer is falling. 
2nd Observation.—The level of the lake having been carefully 
watched subsequent to the changes observed on the 4th October, it 
is improbable that any variation took place until the second obser- 
vations, which are as follows :— 
During the night of the 7th and morning of the 8th December, 
a heavy gale was blowing from the N.W., the barometer standing 
at 29:20” in themorning. Between 11 a.m. and noon the lake was 
rising and falling steadily, the amplitude of the seiche being 0°8 
inches; this amplitude was reduced to 4 inches at 4 p.m. 
1 Le Léman ; Monographie limnologique par F. A. Forel, Lausanne ; F. Rouge,1892. 
Note:—The Bibliography is at p. 455, and the chapter on Limnologie gives all that 
is known about seiches. 
2 Barometer readings reduced to sea level. 
